Create Multiple Y Axes for an R Plot

R base graphics is a powerful tool for plotting data.  Sometimes it is convenient to visualize combinations of variables on the same plot.  Often different variables require different scales.  This can be facilitated by using different Y axes, such as a plot with a Y 2 axis on the right hand side.  In R adding a Y axis is very easy to do.  Here are two simple example scripts you can use to build off of.  The first two examples are two different ways of showing different scales for the same variable (i.e. temperature in Farenheit and Celsus).  The third example is two different variables overlaid on the same R plot with two Y axes used to show the scales of each variable.